PEP 641: Using an underscore in the version portion of Python 3.10 compatibility tags

PEPs
6

The difference is not large.

'%d%02d' % (major, minor)

vs

'%d_%d' % (major, minor)

And parsing:

major = int(version[:-2])
minor = int(version[-2:])

vs

major, minor = version.split('_')
major = int(major)
minor = int(minor)

Also, the advantage is that int('4_1') < int('3_10'), but int('310') < int('401').